The three men, along with five other Britons, chartered a salvage ship in 2000 and bought a £2,500 licence to retrieve tin ingots from the Glen Logan, a British merchant ship torpedoed by a U-boat in 1916 near the island of Stromboli in the Tyrrhenian Sea.

However, instead of working on the Glen Logan, the men diverted their course 460 miles north and found the wreck of the 150ft Pollux.

Pascal Kainac, a historian from Paris, will also stand trial today at Portoferraio in Elba for supplying the men with the ancient maps and co-ordinates to help them find the Pollux.

After three weeks of diving, the men recovered 311 French and Spanish gold coins, 2,000 silver coins, some diamonds and other pieces of jewellery.

The Pollux sank in just 15 minutes after being hit by another steam ship. According to reports at the time, the ship carried 100,000 gold coins, 70,000 silver ones and "a gold carriage belonging to the Contessa de la Rocca". There were also rumours that the other steam ship was manned by pirates.

Although the Pollux's owner mounted several rescue missions for it during the 1840s, he eventually conceded that the boat was lying too deeply to be retrieved. The British divers, who deny wrongdoing, were arrested after irregularities in their paperwork tipped off the Receiver of the Wreck, based at the Maritime and Coastguard Agency in Southampton.

A joint investigation by Scotland Yard and the office of Italian Patrimony in Florence followed.

The men were about to sell the treasure, which they claimed they had found in international waters, at an auction house in Bond Street. Instead, the coins and jewellery were confiscated and returned to Italy, where they will go on display at a museum in Elba.

Mr Pearson, a property developer from Great Yarmouth, maintains that the divers have been the victims of a bureaucratic mistake. He has said their activities had been "declared correctly with the British Government" and that Italian authorities had visited their salvage vessel every day during the project.

Mr Sinclair, a diver from Corton near Lowestoft, said: "Blood, sweat and tears went into getting it and we lost it on a technicality."

Cesarina Barghini, the Italian lawyer defending the men said the rules surrounding the dive permits were very complex.

In Britain, the men were given a warning and a fine. In Italy, prosecutors have spent years assembling a case against them.

Giuseppe Rizzo, the state prosecutor in Elba, said: "These divers tricked their way on to the wreck and submitted false paperwork. They took items which belong to Italy from the ship and they also damaged the vessel."

If found guilty, Pearson, Sinclair and Dixon, a marine consultant from Aylsham, Norfolk, face up to four years in jail.

Mr Sinclair said: "I thought this was all over. I'm sorry for what happened and we did give everything back."